The present invention relates to a electromagnetic filter that uses coupling devices to transmit an electromagnetic wave from the filter input to the filter output through a plurality of resonator cavities.
A bandpass filter passes frequencies falling within a specified band of frequencies. A microwave resonator filter is a particular type of bandpass filter that is used in communications systems on Earth and in space. Such systems include cellular, PCS, and satellite systems. Microwave resonator filters are particularly useful in spaced-based applications where the mass, volume, and electrical performance of the filter are of critical importance.
A prior art microwave resonator filter 10 is shown schematically in FIG. 1-3. The filter 10 includes an enclosure structure 12 which defines first and second cavities 14 and 16. The cavities 14 and 16 contain first and second resonators 18 and 20, respectively.
An electromagnetic ("EM") wave is received by the filter 10 through an input device 22 which is coupled to the first resonator 18. The EM wave is transmitted to the second resonator 20 through a coupling member 24, and is transmitted from the filter 10 by an output device 26, which is coupled to the second resonator 20. The structure of the cavities 14, 16, the resonators 18, 20, and the coupling member 24 affect the frequency response of the filter 10, as is known in this art.
The enclosure 12 includes a peripheral outer wall 28, an inner wall 30, a base wall 32 and a removable closure wall 34. The inner wall 30 is shorter than the outer wall 28 such that a gap 35 (FIG. 2) is defined between the inner wall 30 and the closure wall 34. As shown in FIG. 3, the coupling member 24 is a wire surrounded by an insulating material 36. A holding device 38 holds the coupling member 24 beneath the closure wall 34 in a position extending longitudinally between the two cavities 14 and 16 through the gap 35. The positioning of the coupling member 24 affects the transmission of the electromagnetic wave between the resonators 18 and 20 in the cavities 14 and 16. Therefore, the coupling element 24 must be positioned precisely relative to the resonators 18 and 20.